There is a requirement in many cases for a shaft which is mounted on bearings to have a device attached to the shaft which prevents reverse rotation of the shaft.
This is particularly required in regard to the shaft for carrying a fan since the fan has a tendency to rotate in the reverse direction when there is no drive to the motor due to reverse air flow through the fan. When the air flow is particularly strong, a significant reverse rotation can be obtained which can lead to damage of the motor and/or motor drive components when the motor is started for rotating the fan in the required drive direction. However the present invention is not limited to such arrangements using a fan and can be used wherever such a device is required.
Previous designs have been proposed for mounting on a shaft a device for preventing reverse rotation. One example is manufactured by Twin City Fan and Blower of Minneapolis, Minn. and the construction of this device is described in more detail herein after.
Basically the Twin City device includes a wing member mounted on the shaft which is thrown outwardly by rotation of the shaft due to its weight which retracts a portion of the wing member to prevent that portion engaging a stop which is in fixed position relative to the shaft.
This arrangement has some disadvantages particularly that it can only be used only in a horizontal orientation of the shaft because in the vertical orientation there is no force tending to move the wing member to the abutment position for abutting the stop to prevent the reverse rotation. Also the construction of the Twin City device is relatively complex leading to a higher cost construction.